The present invention relates to brazable articles, and more particularly to a brazable in air diamond tool insert fabricated from a diamond substrate having a bond coat deposited thereon.
The use of diamond tools in the superabrasives market is widespread. Diamond inserts can be fabricated from natural monocrystalline diamond, sintered polycrystalline diamond (PCD) blanks often referred to as compacts, or thermally stable diamond (TSD). More recently, polycrystalline diamond sheets prepared by CVD have been used as diamond tool inserts.
Diamond is often bonded to tungsten carbide tools to improve the performance of the tool. The greatest impediment to the use of diamond in tools is the difficulty of achieving adequate bond between the diamond and the cemented tungsten carbide tool base used to give strength to the tool. Thermal oxidation of diamond above about 700.degree. C. is the chief limiting factor to the achievement of an adequate bond. Typically, bonding is carried out at temperatures of 1000.degree.-1200.degree. C. in a controlled vacuum using braze alloys that contain transition metals to give adhesion to the diamond. Careful control of the oxygen partial pressure is required to prevent oxidation of the diamond and the transition metals.
While this high temperature brazing process gives satisfactory results, it is difficult to manage in production, uses expensive and often brittle brazes, and requires expensive equipment not usually found in the manufacturing environment in which the tools are used. There is a great need in the industry, therefore, for a diamond tool insert that can be brazed in air with standard low temperature brazes. To enable the brazing of diamond in air a coating material is needed that will bond to diamond and make a good metallurgical bond to the braze in an oxygen containing environment.
The prior art is deficient in satisfactory techniques for brazing diamond, especially CVD diamond, to tools. Prior art approaches taken to bonding of diamond to tools generally fall into three categories: geometric effects, coatings or intermediate layers, and brazes. For example, U.S. Pat. No. 4,931,363 discloses the use of high temperature brazes containing chromium for improved bonding of diamond compacts to tungsten carbide tools. European Patent Application, Publication No. 0 402 671 discloses the use of high temperature carbide forming brazes to bond CVD diamond. Each of these, however, require high temperature brazes that must be bonded in controlled vacuum environments.
In U.S. Pat. Nos. 4,649,992, 4,661,180, 4,767,050, and 4,784,023, various geometric approaches to improving adhesion are presented, for example, frustoconical shapes, interlocking alternating ridges, and pocketed substrates. These approaches, however, still require expensive high temperature brazes and vacuum processing.
The use of coatings and interlayers is also disclosed in the prior art. For example, U.S. Pat. No. 4,776,862 discloses the use of carbide forming transition metals as coatings on powders that are then brazed. U.S. Pat. No. 5,037,704 discloses the use of transition metal carbide formers as coatings on compacts prior to protective brazing. United Kingdom Patent Application, Publication No. GB 2 091 763 discloses the use of carbide forming transition metals as additives to abrasive powders during high pressure and temperature sintering. Finally, Japanese Kokai Patent Application No. HEI 4[1992]-21004 discloses the use of a thick transition metal layer, typically 1-5 mm, between diamond and tool substrates prior to brazing in vacuum, typically at 1100.degree. C. While these references disclose the use of transition metals to improve adhesion to diamond, they do not address the issue of brazing in air.
As mentioned above, the greatest impediment to the use of diamond in tools is the difficulty of achieving adequate bond between the diamond and the cemented tungsten carbide tool base which is used to give strength to the tool. Thermal oxidation of diamond above about 700.degree. C. is the chief limiting factor to the achievement of an adequate bond. It would be desirable, particularly for on site replacement of worn diamond tool inserts, to have a diamond insert brazable in an air environment using a standard low temperature braze alloy.
It is an object of the present invention to provide a diamond article which may be directly brazed to a tool body in air.
It is another object of the present invention provide a diamond article which may be strongly bonded to a tool body with low temperature braze.
It is another object to alter the surface of a diamond article so that a strong brazed joint may be easily formed at the work location.
Other and additional objects will become apparent from the description of the invention as set forth herein.